Fiber Distributed Data Interface (FDDI)

The FDDI specifications define a family of standards for 100 Mbps fiber optic LANs that provide the physical layers and media access control sublayer of the data link layer, as defined by the ISO/OSI Model.

IP-FDDI defines the encapsulating of IP datagrams and ARP requests and replies in FDDI frames.

All frames are transmitted in standard IEEE 802.2 LLC Type 1 Unnumbered Information format, with the DSAP and SSAP fields of the 802.2 header set to the assigned global SAP value for SNAP (decimal 170). The 24-bit Organization Code in the SNAP header is set to zero, and the remaining 16 bits are the EtherType from Assigned Numbers:
  • 2048 for IP
  • 2054 for ARP

Typically, the MTU is set to 4352.

Mapping of 32-bit internet addresses to 48-bit FDDI addresses is done by the ARP dynamic discovery procedure. The broadcast internet addresses (whose <host address> is set to all ones) are mapped to the broadcast FDDI addresses (all ones).

IP datagrams are transmitted as a series of 8-bit bytes using the usual TCP/IP transmission order called big-endian or network byte order.

For more information about FDDI architecture, see LAN Concepts and Products.